The recent trend in locks has been toward arrangements where the traditionally used mechanical key and lock are avoided. Actuating devices have been devised for obviating a key so as to prevent tampering with the lock as has become a problem with mechanical-key actuated locks.
The simplest of these devices employs an electrical signal to actuate a relay capable of operating the latch. A complicated device is triggered by a radio signal of a predetermined frequency which is detected by a tuned coil and analyzed by a circuit to operate the latch. A device is also known wherein a printed-circuit card carries a key circuit and has a plurality of terminals exposed along one edge and fittable into a socket connected to further circuitry that opens the latch when this circuitry ascertains that the circuit on the magnetic card corresponds to the key circuit.
These devices have several disadvantages. The use of an expensive radio transmitter greatly elevates the cost of the lock system, as does that of a complex computer to read a circuit-carrying card. Coils of the radio system can become saturated due to induction from transients or parasitic currents. The card-type system can be overcome by obstructing the passage so as to make the card completely uninsertable, or by temporarily borrowing a card so as to decipher the circuit thereon.
It has been suggested to simplify and lower the cost of such devices by employing a key-operated switch of the mechanical type which in turn operates a latch. In such an arrangement an extremely sophisticated key of very complex bitting is employed to minimize the possibility of the lock being picked, and the latch itself is normally in a completely tamperproof location. Such an arrangement has, however, numerous disadvantages of the mechanical-type lock along with many of the disadvantages of the electrical lock. It does have the advantage of relatively low cost, but this alone has not proven to be a strong enough factor to warrant widespread use of such a lock.